Most pulp and paper mills conventionally are provided with chemical recovery boilers. The chemical recovery boiler is basically a steam generating power boiler wherein a molten bed of solids, including black liquor, a by-product of the wood digesting process, is present at the bottom of the boiler. The need arises for the operator to be aware of various conditions within the boiler such as configuration and height of the smelt bed, for both economic and safety reasons.
Typically, various instruments are mounted through a port in the boiler wall to monitor and control the system operation. Viewing means such as a camera, or pyrometer, for supplying a remote image or record, is mounted exteriorly of the boiler and includes a lens or probe extending into a port in the boiler wall. The black liquor in the boiler interior frequently slags over the interior of the port, obscuring the field of view or signal of the instrument lens or probe which often damages the sensing equipment or at least compromises the signal therefrom. The need arises for means to efficiently and reliably remove slag from the boiler port and for any instrument therein.